Means for generating a pulse in a cathode ray tube



Feb. 8, 1938.. A. H. BROLLY 2,107,778

MEANS FOR GENEEMTING A PULSE IN A CATHODE RAY TUBE Filed Oct. 16, 1933 2 Sheets-Sheet 1 mman- EE 3/ .27 I

INPUT.

. C 'I \'\:-I 1 $26- INVENTORT ATTORNEY RCH/B 0 h. BROL Y. BY 44 Feb. 8, 1938. A. H. BROLLY A MEANS FOR GENERATING A PULSE IN A CATHODE RAY TUBE Filed Oct. 16, 1953 2 Sheets-She'et 2 64 AMPLIFIER. OUTPUT.

INVENTOR.

CH/B o H. BROLL v. BY r.

ATTORNEY Patented Feb. 8, 1938 MEANS Fon GENERATING A PULSE IN A 1 CATHODE RAY TUBE Archibald H. Brolly, Palo Alto, Calif., assignor to Farnsworth Television Incorporated, a. corporation of California Application October 16, 1933, Serial No. 693,716

. i 4 Claims.

My invention relates to a means and method of generating a pulse in a cathode ray tube, with particular reference to cathode ray tubes used for the transmission and reception of television 6 signals. 4

Among the objects of my invention are: To provide a simple means of generating a pulse in a cathode ray tube; to provide a simple method of generating a pulse in a cathode ray 10 tube; to provide a means and method of generating a synchronizing pulse in a cathode ray image dissector tube; to provide a method of cathode ray tube image dissection and restoration wherein a pulse is generated; to provide a method of modifying a cathode ray beam during the scanning cycle; and to provide a simple and eflicient means and method of producing pulses which may be desirably utilized in the operation of cathode ray television apparatus.

Other objects of my invention willbe apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of my invention herein described, as various forms may be as adopted within the'scope of the claims.

In the drawings which illustrate the methods of my invention as applied to the structure of cathode ray tubes for television, 1

Figure 1 is alongitudinal. sectional view, of

o cathode ray receiving tube, with an associated diagrammatic operating circuit.

Figure 2 is a cross-sectional view taken as indicated by the line 2-2 in Figure 1, showing in an exaggerated and diagrammatic form the paths 3 followed by the cathode ray beam.

3 Figure 3 is a diagrammatic longitudinal section, and operating circuit of television'transmltting apparatus employing a cathode ray image dissector tube.- The tube and circuit, except for 40 the additional structure and circuit of my in- -vention is that disclosed in the application of to provide a pulse at the receiver adapted to 66 modify or extinguish the cathode ray beam dur- (Cl; PIS-7.7).

' ing a portion of the scanning cycle. It is obvious, however, that other uses may be found in the television system for pulses generated by the cathode ray tubes, and the uses shown serve merely as an illustration in describing the means and method of my invention.

-In broad terms my invention comprises in method, the interception of the e'nergy'of a moving cathode ray beam during a portion of its cycle of movement, and the subsequent utilization of the energy thus obtained to generate preferably a synchronizing pulse 'at the transmitter and apulse adapted to modify or extinguish the cathode ray beam at the receiving end. The complete or partial removal of energy in the receiver beam is of great aid where scanning is done at differential speeds, namely, scanned slowly, and returned at high speed. The pulse may be used to remove the return or back lines thus greatly improving the image. I

The apparatus, broadly, is the same in transmitter and receiver. It comprises an electrode placed within the tube in a position as if at one of the edges of the image, the beam being so deflected that-it will contact the electrode at intervals during the scanning cycle. The energy intercepted by the electrode is then transferred through'the proper electrical connectio'nsto be utilized in the preferred manner;

Theterm as if at one of the edges of the image" is used because. of the three dimensional character of the beam. The image has only two I dimensions. The electrode, however, may obviously be placed either at the actualv edge of the image as seen in the cathode ray tube or at substantially any point between the ,image ,and the source of electrons where the beam will fall'on the electrode after it has traversed the image area. The term .image area therefore will be deemed to mean that area occupied by the beam during scansion of the image irrespective of the plane of section.

In Figure 1 my invention is shown as applied to a preferred form of cathode ray receiving tube. An envelope 2 is provided with the usual electron gun comprising a cathode 4, a control grid 5. and apertured anode 6 with their respective leads I, 9, and i0 sealed through the walls.

The apertured anode 6 is directed toward a I luminescent screen l2 deposited on an expanded viewing end I4.

At one side of the image area, placed to intercept the electron beam after it has traversed the area isan intercepting electrode l5, held in place by an electrode support IGand an electrode lead .modulated, the return being at relatively time being unable to affect the image.

l1 passing through the wall to provide external connection.

Scanning oscillators l9 and 20 with their respective coils 2| and 22 are positioned to direct their fields on the beam at substantially right angles to cause the beam to scan the screen l2 cyclically to produce the image. I prefer to use a saw tooth scanning current whereby the beam is moved relatively slowly across the screen 11811 speed, with either modulated or unmodulated energy in the beam.

I prefer to adjust the scanning coils so that an electrode edge 24 is substantially at right angles to the path of the beam during the higher scanning frequency, as shown in Figure 2. Here the path of the beam during the production of the image is shown by a heavy line 25, the return being indicated by the dotted line 26. In normal operation the lines 26 would be of full brilliancy. I prefer, however, to utilize the energy picked up by the intercepting electrode to modify or extinguish entirely the beam during its return. If extinguished, it will not matter whether or not the beam is modulated during that portion of the cycle, whatever the beam may carry during that By extinguishing the beam, therefore, I release that portion of the cycle for the carrying of other currents used elsewhere than in the image, with the assurance that such currents will not afiect the image in any manner.

The circuit which I prefer for utilizing the energy arriving on the intercepting electrode in the receiving tube is shown in Figure 1.

Thecathode 4 is energized through the cathode leads I by a cathode source 21, one side 29 of which goes to ground and to the grounded leg 30 of the input. The live leg 3| of the input passes to the grid 5 of the tube through the blocking condenser 32.

The anode 6 is energized, preferably from a source of high potential not shown through the anode supply wire 34.

The grid 5 is biased to the desired negative potential by a bias source 35, the negative end leading to the grid through a bias resistor 36 and a load impedance resistor 31,. The mid-point 39 between these resistors is connected to the intercepting electrode through a storage condenser 40, and the anode supply wire 34 is also connected to the intercepting electrode through a leak resistor 4|.

In operation, wewill assume that the scanning oscillator, the anode and the cathode are energized, and that a television signal is coming in,

through the input. The scanning oscillators are adjusted to cause the beam to land on the intersecting electrode at the end of each'line while the image is being reconstructed. Theintersecting electrode thus receives a negative charge from the beam each time the beam is applied thereto.

When the tube is energized, the storage condenser 40 charges up from the anode supply 34 through the leak resistor 4|. The leak resistor is of a high value as compared to'the bias resistor 36, and when the negative charge is receivedby theintercepting electrode, it tends to discharge the storage condenser, current then passing through the bias resistor 36. The voltage drop across this resistor created by the current fiow therein is applied to the grid through resistor 31 to block the electron flow.

The beam is thus reduced or totally extinguished as the scanning coils return it across the by the insertion of screen. The storage condenser in the meantime is slowly charging again through the leak resistor 4| until the beam is ready to come back again for the next line. At that time the storage condenser is fully charged, and the grid has returned to the proper bias again. The cycle is repeated at each traversal.

With the proper selection of values for the storage condenser 40, the leak resistor 4| and the bias resistor 36, the beam may be reduced to an average value during the return trip wherein the illumination of. the screen is so small as to be unseen throughout the greater part of the path. It is realized that the illumination will be gradually increasing throughout the return, but the grid may be biased so that as far as the eye is concerned the return to full illumination takes place at the extreme edge of the beam travel.

Some energy will pass through the blocking condenser 32, but as the lead 3| is from the plate of the amplifier, no harm -will be done, a small loss in the energybeing the'only result. As powerful beams are customarily used in tubes of this character, some carrying as high as '75 watts, a considerable amount of energy can be obtained by the interception.

It should also be noted that thesc-anning can be adjusted so that the beam may be modified during thereturn trip of the beam after having scanned the full picture area. This return path is indicated by the diagonal dotted line 42 in Figure 2. i

A pulse may be obtained ina similar manner an intercepting electrode in an image dissector of the generaltype described by Farnsworth in the above-mentioned application.

In the tube therein disclosed, shown in Figure 3, an envelope '44 is provided at one end with a conductive plate 45 covered with an insulator 45, on which is deposited a mosaic of discrete photo-electric islands 41.

At the opposite end of the tube an electron gun assembly is inserted from one side,- comprising a gun cathode 49 backed by a-cathode shield 50, an apertured gun.anode 5| and an apertured finger sleeve 52. The apertures of the gun anode and finger are in line and are directed toward the photo-electric'mosaic.

The entire gun assembly is usually cylindrical in shape and relatively small so that it does not unduly disturb an image thrown on the photoelectric surfaces by an exterior lens 54.

Only a single pair ofscanning coils 55 energized by 'a transmitter scanning oscillator 55 is here shown as the addition of other coils at right angles to the ones shown would only confuse the drawings.

It is also preferable to focus the beam in the plane of the cathode by means of a focusing solenoid 51 energized by a focusing battery 59 controlled by a variable resistance 50.

In operation the cathode is heated by a cathode battery 5|, one side of which is grounded. The

same side leads through a plate wire 52 to the conductive plate. 45. The gun anode is energized by a grounded gun anode battery 64 through an anode resistor 55. The input to the amplifier is taken off across the resistor 35 and battery 34 through a transmitter blocking condenser 65.

It is preferable that the potential of the gun anode battery be relatively low, 50 volts for example.

The flnger' sleeve is energized by a sleeve battery 61, the negative end of which is connected I claim:

to the plate wire 6 which connects cathode and plate.

It is preferable that the potential of the sleeve battery be relatively-high, such as 500 volts.-

In normal operation, a stream of electrons is formed at the gun cathode, and accelerated toward the gun anode, accelerated by the 50 volts potential thereon. A beam of electrons passes through the gun anode aperture and is again accelerated by the 1500 volt potential of the sleeve.

The beam is projected through the sleeve aperture into the main body'of the tube and decel' erates along the decreasing field.

As the electrons in the beam approach the mosaic surface they lose their velocity and if they are not further influenced they wfli return again being re-accelerated along substantially the same path as they had previously taken, to iinally pass through the sleeve aperture, be decelerated by the difference in potential between sleeve and anode,

and land on the anode to be thereby collected.

It is preferable to make the sleeve aperture largertha'n the anode aperture to allow the returning ele'ctro'ns'to reach the'anode, the slight dispersion acquired during. their journey preventing the greater part .of the electrons from cathode throughthe anode getting backto the aperture.

If, however, .an image is projected on the mosaic surface, each discrete particle islosing electrons during scansion, proportional to the illumination of the particle, thus acquiring a positive charge.

Duringscan'sion of the mosaic surface by the beam, electrons will be abstracted therefrom by the charged particles contacted bythe beam, the

number of'return electrons being less by the x number abstracted. The current between anode and cathode, therefore, ,wlll--be proportional to the illumination 01 the particles scanned, but a large amplification is obtained due'to the fact that each, particle is charging during the entire scanning cycle. -A

- positively charged, as for example, by a battery 10, when the beam contacts that electrode the electrons in the beam may be completely, or, if

desired, partially collected. In this case none, or a predetermined quantity will be returned to the anode, thus giving rise to a deiimte pulse n the output circuit. This pulse, being obtainable at will by the positioning of the electrode, at the end of each line, at the end of one complete cycle or both, maybe desirably utilized as asynchronizing pulse in the transmitted signal train going to the receiver.

The above are examples of the means and methods involved in my invention. It is obvious that others within the scope of the appended claims will beapparent to those skilled in the very eflicient dissector tube is thus obtained.v

If a transmitterintercepting electrode." be inserted along one edge of the image area, and

1. In combinationwith a cathode ray tube having an envelope containing an energized anode and-cathode cooperating to produce a beanr of cathode raysand an area scanned by said beam,

a grid positioned to control the energy in said beam, a collecting electrode positioned at the edge of said areaand adaptedto receive energy, from said beam during scansion as a pulse, a condenser circuit, means for charging said condenser by anode potential, means connecting said condenser V to said electrode to be discharged by energy receive'd thereon, a resistor positioned in said circuit means, and means for applying potentials developed by recharging currents passing through said resistor to said grid.

2. In combination with'a cathode ray tube having an envelope containing an energized anode and cathode cooperating to produce a. beam of cathode rays and an area scanned by said beam, a grid positioned to control the energy in said beam, a collecting electrode positioned at theedge of said 'area and adapted to receive energy from said beam during scansion as a pulse, a condenser circuit, means. for continually charging 'said condenser by anode potential, means connectingsaid condenser to said electrode tobe discharged by a pulse received thereon, a resistor positioned in said circuit means, and means for applying'potentials developed by recharging currents passing through said resistor to said grid.

3. In combination with a cathode ray tubehaving an envelope containing an energized anode and cathode cooperating to produce a beamof cathode rays and an area scanned by said beam,

a biasedgrid positioned to control the energy in 'said beam. a collecting electrode positioned atcurrents passing through said resistor to said grid.

4. In combination with a cathode ray tube comprising an evacuated envelopehaving therein .a cathode, a control electrode, and an anode cooperating when energized to produce a modulated beam ofelectrons, an area positioned to intercept said beam, means for-scanning said beam cyclically over said area, collecting means' positioned to intercept energy, from said beam periodically, a'condenser associatedwith said collecting means,- a. highresistance connected between said anode and said'condenser, and a low resistance connected between said condenser and ,said control electrode.

ancnnsam H. BR LLY. 

